Challenges on Solid-State Lighting Offline Driver Design Jerry Zheng VP, Technical Marketing iwatt Inc, Los Gatos, CA jjzheng@iwatt.com
Contents Review the challenges with replacing incandescent lamps Review LED lamp driver basics Approaches to improve power factor Isolated solutions without opto-coupler Dimmable LED driver solutions
SSL LED Lamps @LedEngin Incandescent Lamps DC-LED Lamps Dimmable DC-LED Lamps Pure resistive load Phase-out Simple Switch-mode Power Drivers EMI, Size, Safety Thermal Switch-mode Power Drivers Various Dimmers EMI, Size. Safety, Thermal
Offline LED Lamp Basics Base Optics Offline LED drivers Heatsink LED Emitters Luminous efficacy = (LED luminous efficacy) x (Driver efficiency) x (LED thermal efficiency) x (Optics efficiency) Where LED Luminous Efficacy is visible lumens/optical watt
Offline LED Lamp Driver Topologies Non-isolated Isolated Buck-BoostBoost Flyback buck Linear SEPIC
Driver should be Isolated or Non-isolated? Isolation between AC socket and the exposed surface is required Isolation can be done in the driver board by transformer Or isolation can be done between the emitter and heatsink Or the whole lamp is isolated Isolated here? Isolated drivers Suitable for high-power high-current low-voltage More components, less power efficiency Easy for mechanical design and thermal management Easy for EMI design, Easy for Safety Isolated here? Non-isolated drivers Suitable for low-power high-voltage low-current Simple, low cost Easy for electric driver board design Challenges for EMI and safety
SSL LED Standards Relate to the Driver ENERGY STAR Program Requirements for Integral LED Lamps FCC requirements 47 CFR part 15 Class A and Class B Harmonic Emission limits and related power quality ANSI C82.77-2002 IEC 61000-3-2 Safety UL8750 IEC 60950 Part 1 Line Transient protections ( Lighting Surge) IEEE C62.41-1991; Class A, 100kHz ring wave, 2.5kV combine Audible Noise Class A
Challenges to Promote LED lamp LED lamp challenges to be overcome in order to enter into home lighting market: Cost Driver BOM cost should be below 15% of total lamp cost Thermal efficiency Any milliwatt loss inside driver certainly reduces the efficiency ( lumens per input watt ) and reliability. Reliability and Life time Multi-layer protections for OTP, OCP, short circuit, open circuit Single fault protection for any case Less component count Regulatory and Safety EMI Power Factor and Harmonic Line Isolation and less leakage current Dimmable No visual Flicker Wide Dimming Range
Approaches to Improve Power Factor Basic Flyback: Single-stage Solution Advantage Simple No bulk e-cap Disadvantage Line frequency ripple current Boost + Flyback: Two-stage solutions Advantage No flickers High PF Disadvantage Cost
Simple Passive Valley-fill PFC Circuits Advantage Simple passive solution Low cost Main disadvantage Low efficiency Relative high THD
Example: Valley-fill filter LED Driver iw3620 for 15-30W LED driver 1.2ohm
Measurements: Power Factor and THD Vin 230V PF=0.93 Harmonic 3 rd PF = 15% 5 th _25% cosϕ 1+ THD 2
A simple SEPIC Active High PF Design
Operations
Measurements: Power Factor and THD Active PFC with iw3620 Efficiency Vin 110V PF=0.95 Harmonic 3 rd 22% 5 th _10% Vin 230V PF=0.96 Harmonic 3 rd 20% 5 th _5%
Isolated solutions without Opto-coupler Isolated Solutions has many benefits to optimize the total costperformance tradeoff Opto-coupler is typically used for isolated-solution to control the LED current; It becomes the weak component that reduces the life time of LED lamps. Primary-side constant current regulation eliminates the opto-coupler, and can also precisely control the LED current Benefits on Primary-side control Line Isolation Easy for heat sink design Easy for heat spreading Easy to meet safety regulation More reliable and longer life time No opto No Y-cap High Efficiency design Isolated current transformer is easy for optimize efficiency
Digital Power Control on LED Constant Current Regulation I o I I = pri _ pk pri_ pk = 2 N 2I N o ps ps T T T s rst T rst s Directly use primary current information. K = 2I o _ cc _ k n R sp _ k ss _ k V = ss _ pk _ set _ d K T T s rst
Adaptive Primary-side LED Constant Current Regulation I o = I pri _ pk 2 N ps T T rst s I pri _ pk = 2I N o ps T T s rst +/- 5% Overall constant current regulation Eliminate the impact of Lm, Vin and leakage inductance LED open circuit protection Single fault protections Current overshoot control
Intelligent Digital Power Control Benefits Digital Primary-Feedback Technology Patented No Opto, No TL431, No current sensor, No secondary control circuits Better performance than traditional design Adaptive cycle-by-cycle Digital Regulates Constant Current Multi-layer advanced protection features Isense short protection and other single-point fault protections Brown-out / recovery OVP, UVP, short circuit, More Low cost, Less components More reliable
Example: Low-cost LED Driver for 1~3W (a) (b) iw1696 Demo-Board available upon request (1-2W)
Measurement: Efficiency and Thermal Efficiency Temperature
Example: High Power LED Drivers 5-30W
Measurements Efficiency and V-I curve 87% efficiency 24V@870mA
Challenges For Dimmable LED Driver Requirements The first challenge is to replace the socket of A-lamps with LED lamp, while maintaining compatibility with existing dimmers. Existing wall dimmers are designed to drive purely resistance A-lamp loads. When it drives a capacitive load or current source, the dimmer may not work properly. LED lamp needs to operate with different dimmer types: Leading-edge dimmers, Trailing-edge dimmers, Smart Dimmers In case the LED lamp can not work properly with certain dimmers, the LED lamps should provide certain safety protections to prevent fire, high leakage current etc. Dimming Performance Wide dimming range 1% to 100% No visible Flicker AC-cycle inrush current High Power Factor at maximum dimming level Residential > 0.7 Commercial > 0.9
Knowing Wall Dimmers Dimmer types: Leading-edge Trailing-edge Smart dimmers, adaptive adjust the turn-on angle to minimum the line distortion; could be leading-edge, could be trailing-edge More.. Dimmer impedance and power level also varies R R-L R-C 400W, 600W etc Dimmer with Triac The gate current must remain present until the load current has reached the latch current (IL) and then the triac will remain on until the load current falls below the hold current (IH). This requirement creates the issue for switch-mode power supply where the impedance is not purely resistive (reactive load = current not in phase with voltage).
Knowing Wall Dimmers Trailing edge dimmer When trailing edge dimmer works with low power LED driver, it is difficult to detect the falling edge. Leading edge dimmer The TRIAC has a minimum gate trigger current (IGT) to turn the TRIAC on. It also requires a minimum holding current to hold the TRIAC on once conducting. When the current drops below the holding current, the TRIAC turns off.
A Simple Configuration to Combine the Dimmer Detection and PFC Unique Method to Configure the Dimmer Type Provide the Pure resistive impedance to Wall Dimmer Line current shape to improve power factor Reduce AC-cycle Inrush current
Overview iw3610 Simplified Schematic EMI Chopping Circuit Fly back Controller
Chopping Control Scheme AC Input From dimmer Output _TR Vin _signal Vin _signal Output_ TR
Dimming Detection Smart Dimmer Detection At configuration state, Detect: Leading-edge Trailing-edge No-dimmer LED Current Vcc OUTPUT_TR Trailing-edge VIN Leading-edge Configuration state No-dimmer Fly-back start operating
Thermal Drifting and Protection NTC LED current Vt Voltage
Example: 5W Dimmable LED Lamp Phase detect with boost conversion Dimming control iw3610
Example: 17W Dimmable LED Lamp
Measurements: Efficiency Regulations
Conducted EMI Result 120VAC/60Hz PKScan Peak Scan QP Limit line AVScan AVScan Limit line Test Conditions : LED Full load. Output Ungrounded.
Full Dimmable LED Lighting Solution with Wall Dimmers 75mm 30 mm 56mm 18mm 25mm Wall dimmer 11mm 42mm
Complete Solutions for Indoor General Lighting 35mm 26mm Down Light H=13mm 15mm EFD15 32mm 48mm H=25mm PAR Light GU10 MR16 E14 GU10
Complete Solutions for T8 /T12 T8 15W, 18W, 20W High efficiency > 85% Power factor > 0.9 L x W x H: 230 x 19 x 13 mm
Q &A